In the present specification, regarding sugars and sugar residues as used herein, all optical isomers are D-isomers, unless otherwise indicated.
Chondroitin sulfate and chondroitin are kinds of glycosaminoglycans having, as the fundamental backbone, a repeating structure of a disaccharide of a D-glucuronic acid residue (hereinafter sometimes simply referred to as “glucuronic acid” or “GlcUA”) and an N-acetyl-D-galactosamine residue (hereinafter sometimes simply referred to as “N-acetyl-galactosamine” or “GalNAc”) (i.e., -[GlcUAβ(1,3)-GalNAcβ(1,4)-]n; is an integer of 2 or more).
Until now, glycosaminoglycans, particularly chondroitin and chondroitin sulfate, have been extracted and purified from cartilages, organs and the like in animals. However, due to shortage of the materials, a method for artificially synthesizing a chondroitin backbone common to chondroitin and chondroitin sulfate has been recently studied. Particularly, a method using a human-derived enzyme is preferred since a bio-defense mechanism such as an antigen-antibody reaction does not strongly occur even when the artificially synthesized chondroitin or chondroitin sulfate is contaminated with the enzyme. At present, only one enzyme is known as the enzyme for synthesizing such a chondroitin backbone, particularly an enzyme which is derived from human and has both GlcUA transferring activity and GalNAc transferring activity (J. Biol. Chem., 276, 38721–38726 (2001)).
It is considered that use of a cocktail system containing several types of enzymes is preferred for the synthesis of the chondroitin backbone. This is because the different optimum reaction conditions of respective enzymes can relax the reaction conditions of the general reaction system However, only the above-described enzyme is known at present as an enzyme which is derived from human and has both GlcUA transferring activity and GalNAc transferring activity, and it is the present situation that studies on the synthesis of the chondroitin backbone are insufficient because of the difficulty in strictly controlling the conditions.
Accordingly, a human-derived novel enzyme which is an enzyme for synthesizing a chondroitin backbone and has both GlcUA transferring activity and GalNAc transferring activity has been desired.